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Grey gurnard (Eutrigla gurnadus) in the North Sea: an emerging key predator?

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Abstract:

Grey gurnard (Eutrigla gurnadus) is a widely distributed demersal species in the North Sea that has been ranked frequently among the 10 dominant species. Since the late 1980s, grey gurnard catch rates in the international bottom trawl surveys showed a pronounced increase and it was included as an "other predator" in the North Sea multispecies virtual population analysis (MSVPA) in 1997. The MSVPA results estimated grey gurnard to be responsible for approximately 60% of the total predation mortality on age-0 Atlantic cod (Gadus morhua). Long-term MSVPA predictions led to the extinction of North Sea cod. As a possible technical reason, the Holling type II functional response implemented in the model was discussed. In the current analysis, it was demonstrated that the Holling type II functional response was not responsible for the extinction of cod in the model, which was rather a true effect of high grey gurnard predation. Further, it was shown that grey gurnard predation had a significant top-down effect on whiting (Merlangius merlangus) and potentially also on cod recruitment, which was linked to the spatial distribution of the three species. Eventually, the implications of the results for North Sea cod stock recovery plans were discussed.

Le grondin gris (Eutrigla gunardus) est une espèce démersale à grande répartition dans la mer du Nord, qui a souvent été classée parmi les 10 espèces dominantes. Depuis la fin des années 1980, les taux de captures du grondin gris dans les inventaires internationaux de chaluts de fond ont augmenté de façon marquée et le grondin gris a été inclus parmi les « autres prédateurs » dans l'analyse des populations virtuelles plurispécifiques (MSVPA) de la mer du Nord en 1997. Les résultats de MSVPA estiment que le grondin gris est responsable d'environ 60 % de la mortalité totale due à la prédation chez les morues (Gadus morhua) d'âge 0. Les prédictions à long terme de MSVPA prévoient l'extinction de la morue de la mer du Nord. Nous discutons de l'inclusion de la réponse fonctionnelle de Holling de type II comme raison technique possible de cette extinction. Dans notre analyse, nous démontrons que la réponse fonctionnelle de type II de Holling n'est pas responsable de l'extinction dans le modèle, mais que l'extinction est de fait due à la forte prédation par le grondin gris. De plus, nous montrons que la prédation par le grondin gris a un effet descendant significatif sur le merlan (Merlangius merlangus) et potentiellement aussi sur le recrutement de la morue, qui est lié à la répartition spatiale des trois espèces. Finalement, les conséquences de ces résultats sur la récupération du stock de morues de la mer du Nord font l'objet d'une discussion.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2005-08-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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